This invention relates to precision motors and more particularly to small or miniature-type motors, including stepping motors and the like.
There exists a need for miniature motors which can be produced at low cost, and which inherently maintain a high degree of precision in the location and alignment of the rotating and non-rotating parts. One important aspect in maintaining precision in mass produced motors is that of tolerance in the manufacture of the parts. On the one hand, low cost motors frequently use metal stampings for the magnetic poles, as shown for example in the United States patents of Kavanaugh, U.S. Pat. No. Re. 28,075 issued July 16, 1974, Van Lieshout et al, U.S. Pat. No. 2,981,855 issued Apr. 25, 1961 and Riggs, U.S. Pat. No. 3,014,141 issued Dec. 19, 1961. However, in such conventional constructions, the bearings for supporting the motor shaft and armature are, themselves, supported on end frames or pole members. Accordingly, the bearing-receiving openings in such end frames or pole members must be accurately formed, and their positions maintained in assembly.
It is also known to cement bearing housings directly to a bobbin in the manufacture of watch motors to achieve accurate alignment of the motor shafts, as shown in da Costa et al, U.S. Pat. No. 3,803,430 issued Apr. 9, 1974. In da Costa, no metal individual pole pieces are used.